Improving the fuel efficiency of an agricultural tractor diesel engine

. The main reason for the emergence of the operational characteristics of tractor diesel engines is the uneven fuel consumption. Fuel equipment is one of the most responsible systems of diesel engines. The purpose of the study was to improve the fuel efficiency of an agricultural tractor diesel engine by using an injector sprayer. Modernization of the needle of the atomizer of the fuel injector is carried out by directing its guiding surface of the helical groove at an angle α, advancing the direction of the axisymmetric fuel pressure. This includes the fuel injector needle, as it is likely to be skewed, stuck, and dependent. The novelty of this design is protected by the patent of the Russian Federation RU 2231673. To assess the fuel efficiency, natural experiments of a diesel engine with serial and modernized injectors were carried out. The introduction of new technical equipment in the fuel equipment has led to the achievement of diesel engine power by 8 ... 12% and the rate of retention of fuel consumption by 3 ... 4%.


Introduction
The main part of the costs of agricultural products is accounted for by energy tractors.Universal row-crop tractors perform 80% of the total volume of agricultural work at the present time [1][2].
The conditions and modes of operation of tractor diesel engines are of particular importance.The maximum loading of tractor diesel engines occurs when performing the most energy-intensive technological operations.Loading tractor diesel during sowing and plowing is 75-89%.In this mode, the diesel engine of an agricultural tractor unit operates up to 60% of the total time of use [3][4].
External conditions affect the mode of operation of a diesel engine and lead to a change in performance [5][6] and fuel consumption [7][8][9].More than 60% of agricultural tractor failures are due to diesel engine failure.The deviation of the fuel supply characteristics from the nominal ones in transient and transient conditions leads to a decrease in power and an increase in the specific fuel consumption of diesel engines [10][11].
The reliability of fuel equipment determines the efficiency of diesel engines and their fuel ef-ficiency.Operating conditions affect the change in power, fuel consumption, the number of failures of components and systems and determine the performance of a diesel engine [12][13].
The number of diesel engine failures due to the failure of the lubrication system is 7.6%.The failure of the cooling system is 9.3% of the total number of failures.The power system failure rate is 39.8%.Most often (up to 50%) diesel engine failures are associated with fuel equipment failure.The main share of faults that cause a decrease in the efficiency of the technological process falls on the atomizers of the fuel system injectors, the resource of which varies in a wide range from 500 to 1600 hours [14][15][16].
The low performance of atomizers of injectors of fuel equipment is explained, first of all, by a change in the parameters of the shape and geometry of the working surfaces at the interfaces of the guide cylindrical and locking conical parts of the needle and the injector body [17][18][19].The operating conditions of agricultural tractors contribute to additional contamination of diesel fuel with highly dispersed particles of road and field dust, which has an additional negative impact on the performance of injectors [20].
The main reason for the decrease in the performance of tractor diesel engines is the uneven supply of fuel.Sometimes it reaches 20%.Fuel injection equipment is one of the most critical and least reliable diesel engine systems.Therefore, the issues of modernization of diesel injectors in order to increase the efficiency and performance of diesel engines are of particular relevance [21][22].
The aim of the study is to improve the fuel efficiency of the diesel engine of an agricultural tractor by modernizing the spray nozzle.

Main theoretical provisions
The deviation of the fuel supply from the optimal values is the main reason for the decrease in the fuel efficiency of the diesel engine of agricultural machinery.The main indicators of fuel efficiency are: power and torque of a diesel engine, specific and hourly fuel consumption.
The power of a diesel engine depends on the torque and the engine speed And connects the specific and hourly fuel consumption (2) The cyclic fuel supply has a significant impact on the efficiency and working process of a diesel engine.It depends on the properties of the fuel, the number of injectors and the quality of atomization determined by the design parameters of the atomizers of the injectors.It has been established [23][24][25] that the cyclic supply of fuel depends on: the pressure of the start of fuel injection; hydraulic density of the atomizer; effective flow area and needle travel.
The fuel injection pressure determines the range of the jet, the angle of the cone of the jet and the dispersion of the fuel atomization.Wear on the injector contact surfaces reduces injection pressures.Reducing the injection pressure by 6...7 MPa from the nominal value increases fuel consumption by 20...25% [26][27].
Mechanical impurities in the fuel penetrate into the gap between the needle and the nozzle body.This causes wear and increases the clearance of the working surfaces of the atomizer (0.2…0.8), which reduces its hydraulic density.This worsens the process of fuel mixing, reduces the power and efficiency of the diesel engine [28].
An increase in the stroke of the needle (0.2...0.35 mm) due to poor fuel filtration leads to an increase in fuel consumption.The size of the flow section of the atomizer is directly related to the amount of fuel injected into the combustion chamber.Coking of spray holes by 20...25% leads to a drop in diesel engine power by 6.5...8% [29][30].
Therefore, the design parameters of the injector affect the quality of fuel atomization and allow you to control the efficiency of the diesel engine.The nozzle atomizer has a significant impact on the quality of atomization and the accuracy of fuel dosing [31][32].Thus, the power, performance, efficiency and reliability of a diesel engine depends on the geometrical parameters of the injectors [33][34].
Scientific hypothesis: it is possible to increase the fuel efficiency of a diesel engine by upgrading the injector nozzle of the fuel equipment.

Modernization of the diesel injector atomizer design
It is proposed to make a helical groove at an angle α in the guide part of the atomizer to create an axisymmetric fuel pressure that will flow from the groove into the gap between the housing and the guide part of the atomizer needle (Figure 1).This new technical solution is designed to improve the reliability of the injector when the diesel engine is running.It is protected by a patent of the Russian Federation [35].The diesel injector atomizer contains a housing 1, in which a locking needle 2 is located, having a guide part 3 with helical grooves 4. The helical grooves 4 end with an annular groove 10 separating the helical part from the locking belt.
Fuel under pressure enters through the fuel supply channel 7 to the internal cavity 8 of the body 1, raises the needle 2 and flows out along the bearing part 5 and the obturator part 6 through the nozzle holes 9. Part of the fuel fills the helical grooves 4, the annular groove 10 and the gap be-tween the body 1 and needle 2. The pressure difference causes fuel to flow from the high pressure area (screw channels 4) to the low pressure area (the gap between body 1 and needle 2).This con-tributes to the centering of the needle and reduces its distortion along the entire length of the guide 3. Forced movement of the needle 2 gives it additional stability.Upgrading the needle of the fuel injector atomizer has reduced the likelihood of warping, "sticking" and freezing of the needle.
The helical groove in the guide part of the atomizer of the modernized nozzle contributes to the asymmetric pressure of the liquid flowing from the grooves into the gap between the body and the guide part.Such modernization not only improves the quality of fuel atomization, but also pro-motes uniform wear of the working surfaces of the injector atomizer, which increases the durability of the diesel engine [36][37].
According to the new technical solution, a prototype of the modernized injector was made and experimental studies were carried out.

Experimental studies
Experimental studies were carried out on the example of a tractor diesel engine 4Ch11/12.5(D-240), used on MTZ 80/82 tractors and equipped with a UTN-5 fuel pump and FD-22 injectors in standard and modernized versions.The design of modernized injectors differed from serial ones by the presence of a helical groove on the working surface of the cylindrical part of the atomizer needle at an angle of 40° (Figure 2).The experiment involved 3 complexes (12 pieces) of serial (Figure 2a) and modernized (Figure 2b) injectors.Eight control stages were held for 500 moto-hours.The total operating time of each set of injectors was 4000 hours.Diesel fuel with a temperature of 36-40℃ and a mass density of 0.81…0.82g/cm 3 was used as a working fluid.
The injector parameters were determined on the KI-3333 stand [38][39].Determination of the hydro density of sprayers was carried out in accordance with GOST 8669-82.The PUF-3 device controlled the mobility of the nebulizer needle [40].The measurement of the effective flow area of the injector atomizer was carried out on a KI-22201 stand with a KI-15713 tool kit [41].The effective flow area of the nozzle atomizer was determined by the pressure difference at the beginning and at the end of the injection.The pressure drop was 5 MPa.At the same time, the time from the moment the fuel supply began to the moment the pressure dropped was measured.All experiments were carried out in triplicate.
Based on the results of injector priming on a test stand with a reference fuel pump with a fixed rail, a set of serial injectors was selected, the flow capacity of which differs by no more than ±1 cm 3 per two plunger strokes.The second set was made up of injectors with modernized atomizers.The study of fuel supply parameters was carried out in the diesel engine mode 4Ch11/12.5 on the stand KI-35478 (Figure 3).On the stand KI-35478, the cyclic supply of a high-pressure fuel pump with modernized and serial injector nozzles was determined.To determine the cyclic supply, the high pressure fuel pump operated in two modes:  Nominal mode with rotation speed n=1100 rpm. Overload mode with rotation speed n=850 rpm.
The injection start pressure in all nozzles was 17.8 MPa.The feed rate was controlled by a clock-type tachometer.All parameters were recorded digitally.The average value of the value of the cyclic fuel supply for the sections was determined: (3)

Where
-cyclic fuel supply pump section; -total number of pumping sections.The identity of the fuel supply to the cylinders was estimated by the value of the cyclic supply unevenness (%): Where are maximum, minimum and average value of cyclic fuel supply.
To study the stability of cyclic deliveries in sections of the high-pressure fuel pump, the acquisition of modernized injectors was carried out by sequentially rearranging the injectors for each section.Identity was over 97%.The installation of nozzles for all sections of the pump and all nozzles for one section gave a deviation from the set value of the cyclic fuel supply of 1.5%.The results were digitally displayed on a personal computer screen.
To evaluate the performance characteristics on the brake stand KI-5543 (Figure 4), accelerated tests of a diesel engine with serial and modernized injectors were carried out.
According to GOST 3647-80, diesel fuel "dusty" with quartz powder with an average grain size of 3 ... 14 microns was used in the process of accelerated tests.One ton of fuel accounted for 50 g of abrasive.All diesel fuel passed through serial and modernized atomizers 35 ... 40 times in 10 hours.The tests were carried out in several stages.The operating modes of the nozzles at different stages corresponded to the operating conditions of the fuel equipment of an agricultural tractor:

Results and Discussion
The value of the cyclic feed was used as an indicator of economic efficiency.It has been established that for a 4Ch11/12.5diesel engine, the dependence of the hourly fuel consumption on the cyclic supply and the cleanliness of shaft rotation n is determined by the formula: (5) As a result of the experiment, the speed characteristics of the fuel pump operating in the 4Ch11 / 12.5 (D-240) engine mode with serial and modernized injectors are shown (Figure 5).The analysis (Figure 5) showed that the proposed modernization of the fuel injector atomizers reduced the unevenness of the cyclic fuel supply by 2.5 times.At high speeds and load of the diesel engine at rpm, the unevenness of the cyclic fuel supply of the modernized injectors is no more than 1…2%.Reducing the shaft speed to rpm increases the unevenness to %, which is within acceptable limits.Power (Figure 6) and fuel economy (Figure 7) performance indicators of a diesel engine in the mode of actual operation of an agricultural tractor with serial and modernized nozzles were obtained as a result of accelerated bench tests on a brake stand KI-5543.The power N of a tractor diesel engine with upgraded injector nozzles is 8…12% higher than with serial injector nozzles.Torque M increased by 5…8% due to modernization.At the same time, the specific fuel consumption of a tractor diesel engine with modernized injector nozzles is 3-4% less than with serial injector nozzles.This confirms the improvement in fuel supply parameters due to modernization.
Additionally, the dependence of the specific fuel consumption of a diesel engine with modernized injector nozzles on the operating time in the nominal mode was obtained (Figure 8).

Conclusion
Fuel equipment is one of the most critical and least reliable diesel engine systems.The quality of fuel atomization depends on the properties of the fuel and the design parameters of the nozzle atomizer.The most promising way to increase the durability of injectors is to improve the working surfaces of precision parts.It is possible to increase the fuel efficiency of a diesel engine by upgrading the atomizer needle.
The design of the fuel injector atomizer has been modernized by applying a helical groove on its guide surface at an angle , which contributes to the emergence of axisymmetric fuel pressure.Uneven pressure contributes to the flow of fuel from the groove into the gap between the body and the guide part of the atomizer needle.This gives the fuel injector needle additional stability, as it reduces the likelihood of warping, "sticking" and hanging.The novelty of this design is protected by the patent of the Russian Federation RU 2231673 [35].
Experimental studies with prototypes of modernized injectors confirmed a 2.5-fold decrease in the unevenness of cyclic fuel supply in unsteady operating modes.The power of a tractor diesel engine with upgraded injector nozzles is 8…12% higher than with serial injector nozzles.At the same time, the specific fuel consumption of a tractor diesel engine with modernized injector nozzles is 3-4% less than with serial injector nozzles.
An increase in the fuel efficiency of a diesel engine with modernized atomizers of fuel injectors has been experimentally confirmed.

Fig. 4 .
Fig. 4. General view of the brake tester KI-5543.Stage 1 (nominal mode 80%): duration 8 hours; rotation speed rpm; cyclic supply mm 3 /cycle.Stage 2 (idling 13%): duration 1 hour 18 minutes; rotation speed rpm; cyclic supply mm 3 /cycle.Stage 3 (overload mode 7%): duration 42 minutes; rotation speed rpm; cyclic supply mm 3 /cycle.At the end of each stage, the state of serial and modernized injector nozzles was monitored.At the end of each stage, the state of serial and modernized injector nozzles was monitored.

Fig. 8 .
Fig. 8. Dependence of the specific fuel consumption of a diesel engine with modernized injector nozzles on the operating time in the nominal mode.